Drywall Calculator
Enter the total length and height of the walls, subtract doors and windows, and pick a sheet size to see how many sheets of drywall to buy. Add the ceiling if you are hanging that too.
How to use this drywall calculator
- Measure each wall you will cover and add the lengths together. Enter the total in the wall length box and the ceiling height in the height box.
- If you are hanging the ceiling too, enter its area. Length times width gives it.
- Enter the combined area of doors and windows. Those openings are not covered with board.
- Choose the sheet size you plan to buy. Longer sheets can mean fewer joints, but they are heavier to carry and hang.
- Keep the 10 percent waste or change it, add a price per sheet if you like, and press Calculate.
- Use Copy result or Export CSV to take the count to the store.
How to calculate how much drywall you need
The calculator works out the area to cover and divides it by the area of one sheet.
- Wall area = total wall length (ft) x wall height (ft)
- Area to cover = wall area + ceiling area – area of doors and windows
- Area with waste = area to cover x (1 + waste % / 100)
- Sheets = area with waste / area of one sheet, rounded up
- Cost = sheets x price per sheet
A 4 ft by 8 ft sheet is 32 square feet, a 4 ft by 10 ft sheet is 40 and a 4 ft by 12 ft sheet is 48.
Worked example
A room has 40 ft of wall with 8 ft ceilings, so the wall area is 40 x 8 = 320 sq ft. A door and a window take up 40 sq ft, so the area to cover is 280 sq ft. With 10% waste you need 280 x 1.10 = 308 sq ft. With 4 ft by 8 ft sheets that is 308 / 32 = 9.6, so 10 sheets. At $14.50 per sheet the boards cost 10 x 14.50 = $145.00.
With 4 ft by 12 ft sheets the same room needs 308 / 48 = 6.4, so 7 sheets.
Assumptions & limits
- The walls are plain rectangles with the full height covered. Soffits, bulkheads, stair walls and angled ceilings need their own area added.
- The waste allowance is not a standard. It depends on the layout, the sheet size and the installer.
- The sheet area is nominal. Some sheets have different thicknesses and types, and the calculator does not recommend one.
- The price is your own input. Compound, tape, screws, corner bead and labor are not included.
- Check local building rules for fire-rated or moisture-resistant board where they apply.
Frequently asked questions
How many sheets of drywall do I need for a room?
Find the total wall area, subtract doors and windows, add waste and divide by the sheet area. A room with 320 sq ft of wall and 40 sq ft of openings needs about 10 sheets of 4 ft by 8 ft board with 10 percent waste.
How much waste should I allow for drywall?
Ten percent is a common starting point for a simple room. Rooms with many corners, windows or angled walls need more.
Should I use 4×8 or 4×12 sheets?
Longer sheets mean fewer seams on a long wall, but they are harder to move and need more help to hang. The calculator shows the count for each size so you can compare.
Do I subtract windows and doors?
Yes, if the openings are large. Small openings such as outlet boxes can be ignored. The calculator subtracts whatever area you enter.
How do I include the ceiling?
Multiply the room length by width to get the ceiling area and enter it in the ceiling box. The calculator adds it to the walls before dividing by the sheet size.
Does this include joint compound and screws?
No. It counts sheets only. Ask your supplier or the product label for compound, tape and fastener amounts.
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Last updated: November 2026